Rehabilitative Ultrasound Imaging (US) is a procedure used to evaluate skeletal muscle size and function to inform clinical practice. US has been shown to be a reliable and valid tool for measuring changes in trunk muscle (i.e. abdominal and back muscle) size and activity during sub-maximal contractions in younger populations. Younger adults with low back pain as compared with healthy adults without pain demonstrate smaller back muscle size, lower back muscle activity, and greater back muscle asymmetry (differences in right side compared with left side).